The present application relates generally to electro-optic transmitter and receiver devices and their applications in connection with fiber optic transmission links.
Multi-octave bandwidth fiber optic transmission links using current-modulated laser diodes in optical transmitters may be limited in their dynamic range due to signal distortions. Such signal distortions may include the second-order and third-order distortion products generated in response to the frequency components of the modulation signal that drives the laser diode. In some systems, the second-order and third-order distortions may limit multi-octave bandwidth performance, and the third-order distortion may also limit the sub-octave bandwidth performance.
Most commercial laser diodes typically have limited optical power as well as transfer curves that cause both second-order and third-order distortions. In addition, nonlinear distortions related to fiber dispersion effects can further limit the linearity of a fiber optic transmission system. For example, the second-order distortion induced by the fiber dispersion can be particularly pronounced in long distance fiber links. See, e.g., C. Y. Kuo, “Fundamental Second-Order Nonlinear Distortions in Analog AM CATV Transport Systems Based on Single Frequency Semiconductor Lasers,” Journal of Lightwave Technology, Vol. 10, page 235 (1992). Suppression of such distortions can be technically complex in part because the fiber induced second-order distortion levels are dependent on the RF frequency.
In various applications using fiber optic transmission links, the fundamental laser diode distortions and the fiber related second-order distortions may constitute the primary sources for the adverse nonlinear distortions. Thus, it is desirable to provide techniques for suppressing such distortions in a variety of applications such as in developing high linearity analog AM fiber links. It is also desirable to provide a high dynamic range to meet the continuing needs for a higher power and more linear arrangement in laser diode intensity modulated links used for multi-octave bandwidth applications.